1. Field of the Invention
This invention is concerned with apparatus for coding and controlling signal generation at each of a plurality of write electrodes of output devices. More particularly, this invention is directed to a controller for a matrix printer having a large number of output electrodes that must each be separately energized by a unique voltage pulse to produce a visible pixel of predetermined color.
2. Description of the Prior Art
It is well known that printing can be effected on a suitable recording medium using appropriate electrical signals. Depending upon the nature of the recording medium, the printing may be based upon electrochemical, electrothermal, electroerosion or electrolytic phenomena. Regardless of the underlying basis therefor, printing is achieved by applying a continuous or pulsed electrical signal to one or more write electrodes. In the case of pulse based printing, it is known that the pulses may be controlled by causing variations in pulse width or amplitude.
In all printers that utilize electrosensitive recording mediums, it is possible to effect printing by applying a voltage of sufficient amplitude, over a predetermined time period, to the write styli of the particular printer involved. Thus, the ability to "write" on an electrosensitive recording medium is chiefly a function of the amplitude and/or duration of the voltage pulses applied to the print styli or electrodes and of the particular type of recording medium involved. In those printers where the recording medium is moved during printing, the overwhelming majority thereof relies only on electrode amplitude variations to cause printing, since variations in the relative difference between the speed at which the recording medium is moved and the speed at which a write cycle was formerly completed, including the point or points within a write cycle at which a pixel is started and completed, would cause registration errors that adversely affect print quality unless compensated for. Such compensation is either more expensive than the savings afforded by the use of write pulse width control or requires that the recording medium be slowed appreciably or stopped during the printer's write cycle, which would adversely impact its thruput rate.
Except for this registration problem and the cost or performance penalty required to compensate therefor, the time variation method would find widespread favor as it would allow the use of fully saturated devices and also avoid the need to utilize variable drive voltages for the write electrodes. This, in turn, would result in increased operating efficiency, lower power consumption, and reduced heat buildup and dissipation problems. An example of a current utilization of this method will be found in commonly assigned and copending U.S. Pat. application Ser. No. 323,843, which was filed on Nov. 23, 1981 in the names of J. Pawletko et al.
Prior art attempts to utilize time-varied, constant amplitude pulses are known. One such typical prior art arrangement is described in U.S. Pat. No. 3,441,946 which issued to E. Rudy on Apr. 29, 1969. The Rudy circuitry is intended to supply write signals in a single stylus recorder that uses electrosensitive paper. More particularly, this write control circuitry is adapted to vary the frequency of write pulses as a function of the speed at which the recording medium is driven under the print stylus. Thus, the designer is able to compensate for differing recording conditions and speeds and control the degree to which the medium is marked.
U.S. Pat. No. 3,553,718, which issued to A. Schierhorst et al, on Jan. 5, 1971, describes another prior art printer wherein time-based control of a write electrode is employed. In Schierhorst et al, a constant amplitude current pulse is sequentially applied to a plurality of write styli, the duration of said pulse being proportional to the signal to be recorded so that the shading of the recording represents the amplitude of the signal.
U.S. Pat. No. 3,613,103, which was issued to C. Harris on Oct. 12, 1971, is also of interest for its teaching of an electrolytic recorder wherein an analog signal to be recorded is converted to a series of pulses with rises spaced in inverse proportion to the amplitude of the analog signal. Control circuitry therefor is adapted to create this pulse series and thereafter utilize the same to trigger a pulse generator whose output is a corresponding series of constant amplitude write pulses having a spatial density that is proportional to the original signal amplitude.
U.S. Pat. No. 3,846,801, which was granted to H. DuMont et al on Nov. 5, 1974, is yet another typical prior art effort that utilizes time-based printing control. Specifically, DuMont et al describes an arrangement for sequentially activating a multiplicity of juxtaposed writing electrodes. To produce the sequential operation of the write electrodes, a time-division demultiplexer is used to distribute time subdivisions of the signal to the respective electrodes. The DuMont et al control arrangement is further adapted so that the write electrodes are activated for just one pulse each during any one clock period.
It has been demonstrated that multicolor electrolytic printing can be accomplished by the judicious use of an appropriate dye matrix, applied to or incorporated in the surface layer of a recording medium. Each dye in the matrix produces a different color when electrolytically excited by a unique pulse, each of these unique pulses having a different threshold amplitude or width that toggles color, that is, a different excitation profile. Unfortunately, none of the foregoing prior art write electrode control arrangements are suitable for use in an operating environment that requires image coding and control of both amplitude and pulse width regulated write pulses, particularly to achieve multicolored printing. For an example of one prior art effort to electrolytically obtain such printing capability and control means therefor, see U.S. Pat. No. 3,654,095, which was granted to D. Koontz et al on Apr. 4, 1972. Furthermore, none of the prior art devices are readily employable in a matrix printer having a large number of electrodes, on the order of at least several hundred, particularly where the actual printing operation is accomplished with a continuously moving recording medium. Such devices would either cause unacceptable print registration errors or simply not be adaptable to the requirements of current matrix printers that might print multicolored documents by simultaneously energizing a large number of print electrodes with one of several unique write pulses.